HomeSS 2GeographyACTION OF WINDS CONTENT

ACTION OF WINDS CONTENT

WEEK 3

CLASS:    SS 2   

DATE: …………………………..

SUBJECT:    GEOGRAPHY

TOPIC:   

ACTION OF WINDS CONTENT:

  1. Processes of wind erosion
  2. Features of wind erosion and their mode of formation. SUB-TOPIC 1: PROCESSES OF WIND EROSION

Erosion takes place mainly by winds in deserts. Wind erosion involves the removal or wearing away of rocks in desert by wind energy or blowing wind.

The main agent of erosion in the desert is the wind. Wind erosion takes place through the process of (i) Deflation (ii) Abrasion (iii) Attrition

  1. DEFLATION: This is the lifting and blowing away of loose sand and pebbles by wind. Deflation results in the lowering of the land surface to form large depressions called deflation hollows.
  2. ABRASION: This is the process whereby sand particles carried by wind are used to blast or wear away rock surface as in rock pedestal, zeugen and yardang.
  3. ATTRITION: This is the process whereby wind borne particles collide with one another, resulting in the wearing away of each other. This results in the reduced round sizes of the particles.

EVALUATION

  1. What is wind erosion?
  2. Name and describe 3 process of wind erosion.

SUB-TOPIC 2:

FEATURES OF WIND EROSION AND THEIR MODE OF FORMATION

As the wind removes or wears away rock in the desert through the processes of deflation, abrasion and attrition certain features are formed. The following are some of the features of wind erosion:

  1. Rock Pedestals or Mushroom Rocks: The sand blasting effect of winds against any projecting rock masses wears back the softer layer so that an irregular edge is formed on the alternate bands of hard and soft rocks. Continuous wind abrasion produces a mushroom like rock called rock pedestals. They are common in the Tibetan Mountains of Central Sahara desert and the devil’s rock in Niger Republic.

 

Rock pedestal

  1. Zeugen: These are tabular masses which have a layer of soft rock lying beneath a surface layer of a more resistance rock. The effect of wind abrasion wears them into a ridge and furrow landscape. Examples are found in Northern Nigeria, Kalahari Desert and Western Australia.

 

Zeugens

  1. Yardang: These are formed when bands of resistant (hard) and weak (soft) rock lie parallel to the prevailing winds. Wind abrasion produces other types of ridge and furrow landscape. The soft bands of rock are removed more easily into passage ways while the hard bands remain standing. They are in short form when hard and soft rocks in vertical bands are in the direction of prevailing winds. The hard rocks standing are called yardang. Examples are in Sallah (Central Algeria), Atacama Desert (Mexico) etc.

 

Yardang

  1. Mesas and Buttes: As a result of action of denudation, the hard top layer of rock resists agents of denudation and protects the softer layers of rocks below from being eroded. At times Mesas may be formed in canyon regions. Canyon develops in the space between Mesas and Butte. Denudation sometimes may reduce mesas in some areas to become isolated fat-topped hill called buttes. They are common in the Arizona region and in South Africa.

 

Mesa and Butte

  1. Inselbergs: This is a residual hill commonly found in desert regions. It usually rises abruptly from level ground and is characterised by steep slopes and round top. Inselbergs are generally believed to be remains of hills, plateaux which have been cut down to their present height by water and wind erosion. Examples are in Kalahari Desert and Northern Nigeria.

 

Inselberg

  1. Deflation Hollows: Its formation involves the lifting and blowing away of loosed materials from the ground in the desert by strong wind, resulting in two strong winds struggling to pass over each other. The loosed materials may be carried in the air or rolled on the ground. The movement in the air or rolling along the ground depends on the size of the materials. The fine particles may be carried in the air far away from the desert to another location outside the desert. Deflation lowers the surface and may eventually form a depression called deflation hollow. Example of such deflation hollow is the Quattara depression in Egypt (Sahara desert).

 

Deflation Hollows

  1. Ventifacts: They are wind polished and faceted or sharpened pieces of pebbles or stones which vary in size from large boulders to small stones. Such rock fragments which are too heavy to be moved by the winds are planned on the windward side. Wind abrasion shapes and polished the pebbles; and new facets develop when wind direction changes. Ventifacts may have one or more than one face or facet. A good example is that of Sahara which has three faces and is called dreinkater (German: three faces). When it has one face it is called einkater (German: one face). An einkater implies that wind direction is constant and always blowing from one direction hence only one face is planned.

 

Ventifacts

EVALUATION

  1. What is the main agent of erosion in deserts?
  2. Name and describe 3 processes of wind erosion.
  3. Describe how Yardangs are formed.

GENERAL EVALUATION 

  1. Describe wind Abrasion.
  2. Using relevant diagram, describe the formation of rock pedestal. 3. What are Zeugens? Describe how Zeugens are formed.
  3. How are Mesas and Buttes formed?
  4. Describe Inselbergs and give examples of where they can be found. 6. Write explanatory notes on deflation hollow.

WEEKEND ASSIGNMENT

Objective Test

  1. Wind erosion takes place mainly in (a) desert (b) rivers (c) ocean (d) streams (e) lakes.
  2. One of the processes of wind erosion is called (a) deposition (b) deflation (c) Zeugens (d) Canyon (e) Pebbles.
  3. Deflation is (a)Lifting and blowing of loose sand and pebbles (b) deposition of sand on hills (c) rainfall in desert regions (d) a resistant rocks (e) not a process of wind erosion.
  4. Yardang is formed when (a) rain destroys houses (b) there is no sunshine (c) hard and soft rocks in vertical bands are in the direction of prevailing winds. (d) There is too much water (e) there are no prevailing winds.
  5. One of the following is not a feature of wind erosion (a) Zeugen (b) yardage (c) inselberg (d) mesa and butte (e) seif dune
  6. Ventifacts are products of (A) sand blasting (B) wind abrasion (C) sheet erosion (D) wind depression.

ESSAY QUESTION

  1. Explain the mode of formation and characteristics of Yardang.

READING ASSIGNMENT:

Read about wind deposition.

REFERENCE TEXT

  1. Essential Geography for Senior Secondary Schools by O.A. Iwena
  2. Comprehensive Geography for Senior Secondary Schools by Peter Oluwafemi. 3. Exam Focus Geography for WASSCE and SSCE by O. Areola et al.
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